Football is a complex contact sport requiring a variety of skills and movement patterns. Due to the considerable physical demands placed on the athlete during football practice and in games, participants are highly susceptible to musculoskeletal injury, with the majority of incidents involving the lower extremity (eg, ankle ligament sprains or anterior cruciate ligament trauma).1 Following injury, appropriate evaluation and treatment are vital to return an athlete quickly and safely to sport. To assess readiness to return to sport, functional tests are administered both during rehabilitation and prior to discharge.2 The functional tests should provide qualitative and quantitative information about movement patterns specific to sport.3,4 To evaluate functional testing, consideration should be given to the types of sport-specific tests to include.4–6
There is a plethora of information on individual functional tests in the literature, but limited evidence is available to help clinicians determine what should be included in a lower extremity functional test battery. Of the studies in the literature that included a battery of lower extremity tests, two2,7 combined several components specific to a sport. The Lower Extremity Functional Test (LEFT)4 involved a combination of an anaerobic activity and sport-specific movements of running, side shuffling, and cutting. The Carolina Functional Performance Index (CFPI)7 has been used to evaluate lower extremity performance in athletes participating in lower extremity dependent sports and includes the co-contraction test, Carioca test, shuttle run test, and single leg hop for time test.
Test selection for athletes who participate in high-risk sports should address power, strength, landing kinetics, and coordination.8 The Functional Performance Test (FPT), a prototype of the CFPI,7 is a functional battery that has been used in the clinical setting for guiding discharge planning for football players and other athletes who may be at risk for lower extremity sport injuries. The FPT was developed to assess basic functional movements of sport: sprinting, backpedaling, cutting, jumping, and side shuffling. The components include a shuffle box drill, figure 8, single leg hop,9–11 Carioca,12 and single leg triple hop measured for distance test.10,13 Despite the clinical use of the FPT, reports on the reliability of the FPT is currently unknown. The purpose of this study was to establish test–retest reliability measures of the FPT.
This study was conducted using a test–retest design to establish reliability. The components of the FPT included the box shuffle drill, figure 8, single leg hop, Carioca, and single leg triple hop for distance tests. Test familiarization occurred 1 week prior to the first scoring session. Athletes performed each test during this initial session. The first testing session was performed 1 week later with trials collected at the same location. The second testing session occurred 1 week later. During both testing sessions, each participant performed the FPT using maximum effort.
A sample of convenience consisting of 62 Division II football players from a mid-Atlantic institution volunteered to participate in this study during their off-season. All participants had to be current members of the football team. Participants were excluded from testing if they had a lower extremity injury in the past 6 months, wore bracing when participating in a sport, had a history of cardiac pathology, or had a diagnosis of uncontrolled asthma. Eight players were excluded from testing because they did not meet the inclusion criteria, leaving a final participant sample of 54. All participants were representative of most football positions based on skill set and functional movement patterns for offense, defense, and special teams. Forty-seven of the 54 participants (seven participants did not return for the second testing session) completed testing with a mean age of 19.77 ± 1.43 years (range: 18 to 23 years), a mass of 101.38 ± 20.08 kg (range: 73.48 to 147.87 kg), and measured 184.45 ± 7.62 cm (range: 167.6 to 198.1 cm) in height. The study was approved by the institution’s Office of Research Compliance.
The following tests from the FPT were administered during each testing session to the exact specifications as reported in the literature: box shuffle drill test,14 figure 8 test,15 bilateral single leg hop test for time,7 Carioca test,7,12 and the bilateral single leg triple hop for distance test.6,10,13 Data were collected at one test site at two sessions separated by 1 week.
Initial First Week Session. Participants participated in a training session 1 week prior to data collection. The training session included a standard dynamic warm-up, a demonstration of the FPT, two submaximal trials, three maximal trials, and a cool-down period. The supervised standard dynamic warm-up required participants to submaximally run .25 mile, followed by static and dynamic stretches for the lower extremity. Static stretches consisted of two repetitions (one on each side) of 30-second holds for the following muscle groups: quadriceps, hamstrings, gastrocnemius/soleus complex, hip abductors, hip adductors, and hip flexors. Dynamic stretches focused on hip abduction, adduction, extension, and flexion maneuvers. The cool-down period consisted of a .25 mile walk followed by the same static stretches described previously.
Testing Sessions. The first testing session was conducted 1 week after the initial training session. Following the standard dynamic warm-up, a 50% and a 75% submaximal trial was performed. Then three maximal effort measurements were recorded, followed by a cool-down period. The second testing session occurred 1 week after the first testing session. The participants were asked to report at the same day and time for each of the testing sessions. Additional physical activity that could affect the results (eg, weight lifting) was monitored by the investigator as closely as possible 24 hours prior to the testing session.
FPT Tests. The FPT was performed in the university’s gymnasium. Equipment required for the performance of these tests included: four plastic cones used as markers indicating the boundaries for the tasks, a standard tape measure, and a standard stopwatch to obtain time measurements. For all tests, three maximal trials were recorded and the best trial of the three was used for data analysis. The best, greatest distance/time, or one successful trial has been used clinically and is followed during National Football League combine testing2,8 (ie, broad jump, vertical jump, single leg hop for distance, crossover hop for distance, triple hop for distance, 6-M timed hop, pro and long shuttle, and agility T-test). If the participant lost balance, missed a target, or fell, the test trial was discarded and repeated. The rest time did not exceed 30 seconds between maximum trials with a 2-minute rest between submaximal and maximal trials for each test. The order of the tests for each participant and for each week was randomized.
Box Shuffle Drill.14 This test was completed by establishing a 10 × 10 yard box using cones as markers indicating the corners. At each cone, the participant changed movement patterns while facing in the same direction during the entire test. The sequence of tasks was to sprint straight ahead, side shuffle to the left, backpedal, and then side shuffle to the right with the athlete ending in the same position as the start point. The stopwatch was started on the participant’s first movement and stopped on return to the start point. Time was recorded to the nearest .01 second.
Figure 8 Test.15 Two cones set 10 yards apart indicated the boundaries. The participant was asked to sprint and go behind the cones in a figure 8 pattern, changing which side of the cone to turn on. The pattern appeared diagonal. The participant completed the test three consecutive times and the time was terminated on return to the start point on the third series of figure eights for each trial. The stopwatch was started on the participant’s first movement and stopped on return to the start point. Time was recorded to the nearest .01 second.
Single Leg Hop Test for Time.7 Two cones were placed 10 yards apart. The participant was asked to change feet when changing directions. The participant hopped for speed on one foot all the way to the opposite cone, quickly changed directions in addition to switching the hopping foot, and went back to the starting cone. The hands were free to move during this test. The stopwatch was started on the participant’s first movement and stopped on return to the start point. Time was recorded to the nearest .01 second.
Carioca Test.7,12 The Carioca step is a sideways movement pattern. The pattern was repeated in a continuous manner for 15 yards. The participant touched the line and returned to the starting cone completing the Carioca step with a different lead foot. The participant faced the same direction the entire time. The stopwatch was started on the participant’s first movement and stopped on return to the start point. Time was recorded to the nearest .01 second.
Single Leg Triple Hop for Distance.6,10,13 This test was measured for distance to the nearest inch. The participant jumped off one foot and landed on the same foot three times before the jumping foot came in contact with the ground for the final time. This was completed bilaterally, jumping as far as possible and measuring for maximal distance from the start point on a single leg to the end position of the same foot after three consecutive jumps. Distance was measured from the starting cone to the athlete’s final position of the toe measured to the nearest inch on completion of the third hop for the single leg triple hop. Because this test is considered a measurement of power, there should not be an increased moment of foot contact with the ground between each jump. The participant was not allowed to use the hands because this would generate momentum, increasing the distance covered. Hands were held behind the back while completing this test. The dominant foot was also noted and was determined by asking each participant which leg would be used to kick a ball.
Descriptive statistics were analyzed for all five components of the FPT. Intraclass correlation coefficients (ICCs) were used to determine test–retest reliability of the FPT by analyzing the maximal effort measurements between test sessions 1 and 2. To determine ICC values for one rater, calculations from a two-way random effects analysis of variance model were incorporated into the ICC3,1- formula according to Shrout and Fleiss16 to determine the test–retest reliability. Guidelines for data interpretation were adopted from Portney and Watkins17 in that an ICC greater than .75 is good, between .75 and .50 is moderate, and below .50 is poor. An ICC of .60 is the minimal acceptable score for reliability.18 The standard error of measurement (SEM)19 was used to determine the precision of the recorded measurements. The SEM demonstrates the variation in expected scores for one participant if the test were repeated multiple times. The following equation was used for SEM as described by Brown19 where S = the standard deviation of the test and rxx = reliability coefficient for the test:
IBM SPSS 21.0 software (IBM/SPSS, Inc., Chicago, IL) was used for the study analyses.
Means and standard deviations for testing sessions 1 and 2, ICC3,1, 95% confidence intervals, and SEM can be found in Table 1. Each component of the FPT had excellent ICC scores and a relatively low SEM. The highest ICC was for the single leg triple hop for distance (ICC = .956), with low SEM values for the right (SEM = 5.975 inches) and left (SEM = 5.890 inches) sides. This was followed by the shuffle box drill (ICC = .933; SEM = .202 seconds), the Carioca (ICC = .930; SEM = .173 seconds), and the figure 8 (ICC = .892; SEM = .329 seconds) tests. The lowest ICC was for the single leg hop for time test (ICC = .873; SEM = .211 seconds). The highest results for SEM were .329 second for the figure 8 and 5.975 inches for the right side single leg triple hop test. Minimal variation was observed within participants on a day-to-day basis when the test was repeated and can be interpreted as the same participant repeating this battery would not deviate more than .5 second or more than 6 inches from his or her best score on any of these tests at any given time.
ICC Scores, SEM, and Means and Standard Deviations Between Weeks
The purpose of this study was to establish test–retest reliability of the FPT for the sport of football. Current findings indicate that the observed reliability for each of the five tests was excellent, ranging from .873 to .956 with low SEMs. These five individual tests had ICC scores that were similar to previous research.4,6,7 Stability in measurement was also determined using SEM. SEM provides the clinician with a way to determine how much variation from day to day should be expected. Therefore, the clinician can determine whether observed changes are real or caused by measurement error. If used in the clinical setting, little variation in measurement from day to day should be expected as determined by the low SEM. Thus, these five tests included in the FPT may be useful as acceptable outcome measures for evaluating the overall functional assessment of the lower extremity using healthy football players when following a standardized protocol.
To our knowledge, this is the first study to report evaluating the reliability of the FPT. Numerous studies have assessed the reliability of both individual tests4–7,10,11 (eg, the single leg vertical jump and single leg hop) and a battery of tests.2,4 However, only one other study7 that incorporated a battery of functional tests with some similarities to the FPT can be used as a basis of comparison. The prototype of the FPT is the Carolina Functional Performance Index (CFPI).7 The CFPI is used to evaluate lower extremity performance in athletes participating in lower extremity dependent sports and included the co-contraction test, Carioca test, shuttle run test, and single leg hop for time test. The index was intended to be used for comparison between pre-injury (used as baseline) and post-injury to track rehabilitation progress. ICCs were determined by McGee and Futtrell7 in a study evaluating reliability for the use of the CFPI by male and female collegiate athletes. Reliability testing was good for the single leg hop test. In examining the co-contraction semicircular test, Carioca test, and shuttle run test,7 ICC scores ranged from .92 to .96.
The CFPI and the FPT only share two tests: the single leg hop for time and the Carioca. Reliability was determined for the single leg hop for time and Carioca tests by McGee and Futtrell.7 The ICCs for both studies were comparable, with results in the good and high ranges except for the single leg hop for time. The single leg hop for time used in the CFPI and this functional test is different from what is reported in the literature.5 The variation in reliability is partially explained by the difference in testing technique for the single leg hop for time. The single leg hop test that is described in most of the literature5,6 is a hop for time with no change in direction or change in feet. Clinically, most complete the test twice, once for each side. However, the CFPI and the FPT single leg hop for time are described in a manner in which both sides can be assessed simultaneously. McGee and Futtrell7 described the single leg hop test as being modified to include both legs in an effort to eliminate the confounding variables of dominance. It is therefore hypothesized that the change in direction and change in feet results in lower ICC scores but is still acceptable for repeatability.
There are other tests that can be used in football, such as National Football League combine testing2,8 but some of the tests are bilateral in nature rather than unilateral, such as the vertical jump, combination of left and right directional changes (agility t-test and pro and long shuttle), or a preferred-limb/direction is used instead of testing both limbs for the single leg hop tests. Following this format, the tests are used more to evaluate performance in healthy participants for draft status, rather than to detect deficits in functional power, force absorption and postural stability,8 or advancement in a return to play protocol. The FPT, which includes the box shuffle drill test, figure 8 test, bilateral single leg hop test for time, Carioca test, and the bilateral single leg triple hop for distance test, can be used for functional testing based on the consistency of measurement evident with the low SEMs.
Despite several position groups represented, not all position groups were adequately portrayed due to the low number of participants. For the FPT to be useful for all football positions, a study using a larger sample size for position groups should be conducted. Although this battery is currently being used in football, further reliability studies are needed using a larger sample size of football players in different NCAA divisions.
Implications for Clinical Practice
Components in the battery met acceptable outcome measures for evaluating the overall functional assessment of the lower extremity. Using a single test in isolation may not adequately simulate all of the challenging movements an athlete may encounter on the playing field.2 Therefore, inclusion of several different types of functional assessment tests, which is included in the FPT, is important when evaluating the overall functional assessment of the lower extremity. By including football players, the results were a more relevant description of the population that has most often used this battery of tests.
Although this study was conducted using healthy athletes, the FPT may be useful to determine readiness to return to sport following a lower extremity injury. However, further evaluation with injured participants is warranted before using this instrument to track rehabilitation progress.
The data collected from this study support the conclusion that the FPT is a reliable objective measure as a lower extremity functional test. Individually, there was a high degree of reliability for the five components of the FPT. Stability in measurement was also determined using SEM, so the clinician can determine if observed changes are real or caused by measurement error. Although this battery is currently being used in football, this same battery can be used for other sports because the movement patterns are similar.
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- Hickey KC, Quatman CE, Myer GD, Ford KR, Brosky JA, Hewett TE. Methodological report: dynamic field tests used in an NFL combine setting to identify lower-extremity functional asymmetries. J Strength Cond Res. 2009;23:2500–2506. doi:10.1519/JSC.0b013e3181b1f77b [CrossRef]
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- Tabor MA, Davies GJ, Kernozek TW, Negrete RJ, Hudson V. A multicenter study of the test–retest reliability of the lower extremity functional test. J Sport Rehabil. 2002;11:190–201.
- Drouin JM, Riemann BL. Lower extremity functional performance testing, part 1. Athl Ther Today. 2004;9:46–49.
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- McGee MR, Futtrell MD. Functional Testing of Athletes and Non-athletes Using the Carolina Functional Performance Index [master’s thesis]. Chapel Hill, NC: University of North Carolina; 2002.
- Myer GD, Schmitt LC, Brent JL, et al. Utilization of a modified NFL combine testing to identify functional deficits in athletes following ACL reconstruction. J Orthop Sports Phys Ther. 2011;41:377–387. doi:10.2519/jospt.2011.3547 [CrossRef]
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- Hamilton RT, Shultz SJ, Schmitz RJ, Perrin DH. Triple-hop distance as a valid predictor of lower limb strength and power. J Athl Train. 2008;43:144–151. doi:10.4085/1062-6050-43.2.144 [CrossRef]
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ICC Scores, SEM, and Means and Standard Deviations Between Weeks
|COMPONENT||WEEK 1||WEEK 2||ICC||ICC 95% CI||SEM|
|Shuffle box||9.6 ± .7 sec||9.5 ± .8 sec||.93||.88 to .96||± .20 sec|
|Figure 8||15.2 ± .9 sec||15.4 ± .8 sec||.89||.81 to .94||± .31 sec|
|Single leg hop||5.8 ± .6 sec||5.5 ± .5 sec||.87||.77 to .93||± .21 sec|
|Carioca||6.6 ± .6 sec||6.5 ± .6 sec||.93||.87 to .96||± .17 sec|
|Single leg triple hop (in)||R = 229.2 ± 29.6||R = 235.4 ± 27.2||.95||.93 to .97||± (R) 5.97 in|
|L = 232.1 ± 27.6||L = 236.1 ± 28.5||–||–||± (L) 5.89 in|